i think vector art are the best but in the same way it will slow the game too much .also bitmap images get more money than vector for example many companies do games in normal,hd (phone,tablet) so that why they get more money.in vector they will only make one game and it will work in all devices but lower money will paid.

all these are my opinion, if im wrong just say im new at development ^^

Vector graphics require processing power, because they in fact are a set of drawing instructions. The graphics are plotted out. Bitmap graphics, on other hand, can be blitted instantaneously and as such aren't all that demanding on CPU.